由于对接第三方开放平台，官方提供的sdk的加解密方式是mcrypt AES 算法，使用了 32 位的秘钥和 16 位的向量，而现有系统环境是PHP7.2，mcrypt扩展已被弃用，需要换成openssl，在网上找了很多方法不成功，最后终于找到解决方法

mcrypt加解密：

<?php
class Prpcrypt
{
    public $key;
    function __construct($k)
    {
        $this->key = base64_decode($k . "=");
    }
    public function encrypt($text)
    {
        try {
            // 网络字节序
            $size = mcrypt_get_block_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_CBC);
            $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
            $iv = substr($this->key, 0, 16);
            mcrypt_generic_init($module, $this->key, $iv);
            //加密
            $encrypted = mcrypt_generic($module, $text);
            mcrypt_generic_deinit($module);
            mcrypt_module_close($module);
            //print(base64_encode($encrypted));
            //使用BASE64对加密后的字符串进行编码
            return base64_encode($encrypted);
        } catch (Exception $e) {
            print $e;
            return false;
        }
    }
    public function decrypt($encrypted)
    {
        try {
            $ciphertext_dec = base64_decode($encrypted);
            $module = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
            $iv = substr($this->key, 0, 16);
            mcrypt_generic_init($module, $this->key, $iv);
            $decrypted = mdecrypt_generic($module, $ciphertext_dec);
            mcrypt_generic_deinit($module);
            mcrypt_module_close($module);
        } catch (Exception $e) {
            return false;
        }
        return $decrypted;
        
        
    }
    function getRandomStr()
    {
        $str = "";
        $str_pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
        $max = strlen($str_pol) - 1;
        for ($i = 0; $i < 16; $i++) {
            $str .= $str_pol[mt_rand(0, $max)];
        }
        return $str;
    }
}

$k = "abc1237890123456789012345678901234567890abc";
$decrypStr = "hello";
$cryptObj = new Prpcrypt($k);
$ret = $cryptObj->encrypt($decrypStr);

$str = "SR4RIdC6WpiYS00yijC6Wg==";
$ret = $cryptObj->decrypt($str);
var_dump($ret);

openssl加解密

<?php

class Prpcrypt
{
    public $key;
    function __construct($k)
    {
        $this->key = base64_decode($k . "=");
    }
    public function encrypt($text)
    {
        try {
            $iv = substr($this->key, 0, 16);
            $encrypted = openssl_encrypt($text, 'AES-256-CBC', $this->key, OPENSSL_RAW_DATA|OPENSSL_ZERO_PADDING, $iv);
        } catch (Exception $e) {
            print $e;
            return false;
        }
        return base64_encode($encrypted);
    }
    public function decrypt($encrypted)
    {
        try {
            $ciphertext_dec = base64_decode($encrypted);
            $iv = substr($this->key, 0, 16);
            $decrypted = openssl_decrypt($ciphertext_dec, 'AES-256-CBC', $this->key, OPENSSL_RAW_DATA|OPENSSL_ZERO_PADDING,$iv);
        } catch (Exception $e) {
            return false;
        }
        return $decrypted;
        
        
    }
    function getRandomStr()
    {
        $str = "";
        $str_pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
        $max = strlen($str_pol) - 1;
        for ($i = 0; $i < 16; $i++) {
            $str .= $str_pol[mt_rand(0, $max)];
        }
        return $str;
    }
}

$k = "abc1237890123456789012345678901234567890abc";
$decrypStr = "hello";
$cryptObj = new Prpcrypt($k);
$ret = $cryptObj->encrypt($decrypStr);

$str = "SR4RIdC6WpiYS00yijC6Wg==";
$ret = $cryptObj->decrypt($str);
var_dump($ret);